They say dancing keeps you young. Well, we can all take a lesson from 91-year-old spinal surgery patient, Julia Tourtellotte. The vivacious great-great-grandmother recently showed off her moves to an enthusiastic crowd at HCA Healthcare Charleston-based affiliate Trident Medical Center. And they were electric. Tourtellotte educated her physician, neurosurgeon Dr. Sabino DAgostino, on the art…